Other than getting rid of public schools (a discussion for another day), your options are pretty simple. You can't get rid of the guns. Even if the political will was there, there are too many already in circulation, and they are too easy to make, for you to accomplish complete gun confiscation.
Here is my proposal:
- No one shall be forced to carry. However, all teachers so inclined should be allowed to carry.
- If possible, there should be an armed school resource officer in every school. If not possible, for example in many rural schools, and there are no firearms inclined teachers at the school, a firearms inclined teacher should be transferred from another school. The sooner there is an armed response, the better the outcome is for everyone else. They don't even have to win, just slow him down enough for the police to get there.
- Single entry, multiple exits. New construction should be set up so that there is a single point of entry for all buildings, next to a manned entry control point (the secretaries can pull double duty on this one), with each classroom having it's own exit. This also makes sense from a fire safety standpoint. Obviously, you can't do this with old buildings, but that's why this isn't a simple point idea.
- Instead of "hide in place" teach "run and dodge". Get the kids outside ASAP, and running away and dodging, instead of staying in their classroom to get shot like fish in a barrel.